Stimulated bacterioplankton growth and selection for certain bacterial taxa in the vicinity of the ctenophore Mnemiopsis leidyi

Bacterial degradation of ctenophore Mnemiopsis leidyi organic matter

Blooms of gelatinous zooplankton, an important source of protein-rich biomass in coastal waters, often collapse rapidly, releasing large amounts of labile detrital organic matter (OM) into the surrounding water. Although these blooms have the potential to cause major perturbations in the marine ecosystem, their effects on the microbial community and hence on the biogeochemical cycles have yet to be elucidated. We conducted microcosm experiments simulating the scenario experienced by coastal bacterial communities after the decay of a ctenophore (Mnemiopsis leidyi) bloom in the northern Adriatic Sea. Within 24 h, a rapid response of bacterial communities to the M. leidyi OM was observed, characterized by elevated bacterial biomass production and respiration rates. However, compared to our previous microcosm study of jellyfish (Aurelia aurita s.l.), M. leidyi OM degradation was characterized by significantly lower bacterial growth efficiency, meaning that the carbon stored in the OM was mostly respired. Combined metagenomic and metaproteomic analysis indicated that the degradation activity was mainly performed by Pseudoalteromonas, producing a large amount of proteolytic extracellular enzymes and exhibiting high metabolic activity. Interestingly, the reconstructed metagenome-assembled genome (MAG) of Pseudoalteromonas phenolica was almost identical (average nucleotide identity >99%) to the MAG previously reconstructed in our A. aurita microcosm study, despite the fundamental genetic and biochemical differences of the two gelatinous zooplankton species. Taken together, our data suggest that blooms of different gelatinous zooplankton are likely triggering a consistent response from natural bacterial communities, with specific bacterial lineages driving the remineralization of the gelatinous OM.IMPORTANCEJellyfish blooms are increasingly becoming a recurring seasonal event in marine ecosystems, characterized by a rapid build-up of gelatinous biomass that collapses rapidly. Although these blooms have the potential to cause major perturbations, their impact on marine microbial communities is largely unknown. We conducted an incubation experiment simulating a bloom of the ctenophore Mnemiopsis leidyi in the Northern Adriatic, where we investigated the bacterial response to the gelatinous biomass. We found that the bacterial communities actively degraded the gelatinous organic matter, and overall showed a striking similarity to the dynamics previously observed after a simulated bloom of the jellyfish Aurelia aurita s.l. In both cases, we found that a single bacterial species, Pseudoalteromonas phenolica, was responsible for most of the degradation activity. This suggests that blooms of different jellyfish are likely to trigger a consistent response from natural bacterial communities, with specific bacterial species driving the remineralization of gelatinous biomass.

Bacterial Communities Associated With Four Blooming Scyphozoan Jellyfish: Potential Species-Specific Consequences for Marine Organisms and Humans Health

Cnidarians have large surface areas available for colonization by microbial organisms, which serve a multitude of functions in the environment. However, relatively few studies have been conducted on scyphozoan-associated microbial communities. Blooms of scyphozoan species are common worldwide and can have numerous deleterious consequences on the marine ecosystem. Four scyphozoan species, Aurelia coerulea, Cyanea nozakii, Nemopilema nomurai, and Rhopilema esculentum, form large blooms in Chinese seas. In this study, we analyzed the bacterial communities associated with these four jellyfish based on 16S rRNA gene sequencing. We found that the bacterial communities associated with each scyphozoan species were significantly different from each other and from those of the surrounding seawater. There were no significant differences between the bacterial communities associated with different body parts of the four scyphozoan jellyfish. Core bacteria in various compartments of the four scyphozoan taxa comprised 57 OTUs (Operational Taxonomic Units), dominated by genera Mycoplasma, Vibrio, Ralstonia, Tenacibaculum, Shingomonas and Phyllobacterium. FAPROTAX function prediction revealed that jellyfish could influence microbially mediated biogeochemical cycles, compound degradation and transmit pathogens in regions where they proliferate. Finally, Six genera of potentially pathogenic bacteria associated with the scyphozoans were detected: Vibrio, Mycoplasma, Ralstonia, Tenacibaculum, Nautella, and Acinetobacter. Our study suggests that blooms of these four common scyphozoans may cause jellyfish species-specific impacts on element cycling in marine ecosystems, and serve as vectors of pathogenic bacteria to threaten other marine organisms and human health.

Scyphomedusae and Ctenophora of the Eastern Adriatic: Historical Overview and New Data

One of the obstacles to detecting regional trends in jellyfish populations is the lack of a defined baseline. In the Adriatic Sea, the jellyfish fauna (Scyphozoa and Ctenophora) is poorly studied compared to other taxa. Therefore, our goal was to collect and systematize all available data and provide a baseline for future studies. Here we present phenological data and relative abundances of jellyfish based on 2010–2019 scientific surveys and a “citizen science” sighting program along the eastern Adriatic. Inter-annual variability, seasonality and spatial distribution patterns of Scyphomedusae and Ctenophore species were described and compared with existing historical literature. Mass occurrences with a clear seasonal pattern and related to the geographical location were observed for meroplanktonic Scyphomedusae Aurelia solida, Rhizostoma pulmo, and to a lesser extent Chrysaora hysoscella, Cotylorhiza tuberculata and Discomedusa lobata. Holoplanktonic Pelagia noctiluca also formed large aggregations, which were seasonally less predictable and restricted to the central and southern Adriatic. Four species of Ctenophora produced blooms limited to a few areas: Bolinopsis vitrea, Leucothea multicornis, Cestum veneris and the non-native Mnemiopsis leidyi. However, differences between Adriatic subregions have become less pronounced since 2014. Our results suggest that gelatinous organisms are assuming an increasingly important role in the Adriatic ecosystem, which may alter the balance of the food web and lead to harmful and undesirable effects.

Differences in the microbiota of native and non-indigenous gelatinous zooplankton organisms in a low saline environment

The translocation of non-indigenous species (NIS) around the world, especially in marine systems, is increasingly being recognized as a matter of concern. Species translocations have been shown to lead to wide ranging changes in food web structure and functioning. In addition to the direct effects of NIS, they could facilitate the accumulation or translocation of bacteria as part of their microbiomes. The Baltic Sea harbours many non-indigenous species, with most recent detection of the jellyfish Blackfordia virginica and the comb jelly Mnemiopsis leidyi in the low saline southwestern Baltic Sea. In this study, we used a multidisciplinary approach and investigated three gelatinous zooplankton species that co-occur in the same environment and feed on similar zooplankton food sources but show different histories of origin. The aim was to conduct a comparative microbiome analysis of indigenous and non-indigenous gelatinous zooplankton species in the low-saline southwestern Baltic Sea. Next-generation 16S rRNA marker gene sequencing of the V1/V2 region was employed to study the bacterial microbiome compositions. All tested species showed significant differences in their microbiome compositions (one way ANOSIM, R = 1, P < 0.008) with dissimilarities ranging from 85 to 92%. The indigenous jellyfish Aurelia aurita showed the highest bacterial operational taxonomic unit (OTU) richness. The overall differentiation between microbiomes was driven by eight indicator OTUs, which included Mycoplasma and Vibrio species. These bacteria can be problematic, as they include known pathogenic strains that are relevant to human health and aquaculture activities. Our results suggest that the impact assessment of NIS should consider potential pathogenic bacteria, enriched in the environment due to invasion, as potential risks to aquaculture activities.

Effect of invasive ctenophores Mnemiopsis leidyi and Beroe ovata on low trophic webs of the Black Sea ecosystem

The study focuses on the impact of life excretion and mucus released by the "biological pollutants" invasive ctenophore Mnemiopsis leidyi and its predator Beroe ovata on the marine environment and lower trophic levels of the Black Sea ecosystem (bacteria, pico-phytoplankton, nano-autotrophic/heterotrophic flagellates, micro-phytoplankton, chlorophyll a, primary production (PP), micro-zooplankton). The chemical and biological variables were analysed in two sets of lab experiments with natural communities from mesotrophic (Gelendzhik) and eutrophic (Varna) coastal waters. While both species altered the chemical properties of experimental media, exerting structural and functional changes in the low food-web biological compartments, the results showed a stronger effect of B. ovata, most likely related to the measured higher rate of excretion and amount of released mucus. In addition the alterations in the Gelendzhik experiment were more pronounced, indicating that environmental implications on lower food-web are more conspicuous in mesotrophic than in eutrophic coastal waters.

Jellyfish-Associated Microbiome in the Marine Environment: Exploring Its Biotechnological Potential

Despite accumulating evidence of the importance of the jellyfish-associated microbiome to jellyfish, its potential relevance to blue biotechnology has only recently been recognized. In this review, we emphasize the biotechnological potential of host⁻microorganism systems and focus on gelatinous zooplankton as a host for the microbiome with biotechnological potential. The basic characteristics of jellyfish-associated microbial communities, the mechanisms underlying the jellyfish-microbe relationship, and the role/function of the jellyfish-associated microbiome and its biotechnological potential are reviewed. It appears that the jellyfish-associated microbiome is discrete from the microbial community in the ambient seawater, exhibiting a certain degree of specialization with some preferences for specific jellyfish taxa and for specific jellyfish populations, life stages, and body parts. In addition, different sampling approaches and methodologies to study the phylogenetic diversity of the jellyfish-associated microbiome are described and discussed. Finally, some general conclusions are drawn from the existing literature and future research directions are highlighted on the jellyfish-associated microbiome.

Bacteria associated with moon jellyfish during bloom and post-bloom periods in the Gulf of Trieste (northern Adriatic)

Jellyfish are a prominent component of the plankton community. They frequently form conspicuous blooms which may interfere with different human enterprises. Among the aspects that remain understudied are jellyfish associations with microorganisms having potentially important implications for organic matter cycling. To the best of our knowledge, this study is the first to investigate the bacterial community associated with live moon jellyfish (Aurelia solida, Scyohozoa) in the Adriatic Sea. Using 16S rRNA clone libraries and culture-based methods, we have analyzed the bacterial community composition of different body parts: the exumbrella surface, oral arms, and gastric cavity, and investigated possible differences in medusa-associated bacterial community structure at the time of the jellyfish population peak, and during the senescent phase at the end of bloom. Microbiota associated with moon jellyfish was different from ambient seawater bacterial assemblage and varied between different body parts. Betaproteobacteria (Burkholderia, Cupriavidus and Achromobacter) dominated community in the gastral cavity of medusa, while Alphaproteobacteria (Phaeobacter, Ruegeria) and Gammaproteobacteria (Stenotrophomonas, Alteromonas, Pseudoalteromonas and Vibrio) prevailed on ‘outer’ body parts. Bacterial community structure changed during senescent phase, at the end of the jellyfish bloom, showing an increased abundance of Gammaproteobacteria, exclusively Vibrio. The results of cultured bacterial isolates showed the dominance of Gammaproeteobacteria, especially Vibrio and Pseudoalteromonas in all body parts. Our results suggest that jellyfish associated bacterial community might have an important role for the host, and that anthropogenic pollution in the Gulf of Trieste might affect their community structure.

Seasonal Shifts in Bacterial Community Responses to Phytoplankton-Derived Dissolved Organic Matter in the Western Antarctic Peninsula

Bacterial consumption of dissolved organic matter (DOM) drives much of the movement of carbon through the oceanic food web and the global carbon cycle. Understanding complex interactions between bacteria and marine DOM remains an important challenge. We tested the hypothesis that bacterial growth and community succession would respond differently to DOM additions due to seasonal changes in phytoplankton abundance in the environment. Four mesocosm experiments were conducted that spanned the spring transitional period (August-December 2013) in surface waters of the Western Antarctic Peninsula (WAP). Each mesocosm consisted of nearshore surface seawater (50 L) incubated in the laboratory for 10 days. The addition of DOM, in the form of cell-free exudates extracted from Thalassiosira weissflogii diatom cultures led to changes in bacterial abundance, production, and community composition. The timing of each mesocosm experiment (i.e., late winter vs. late spring) influenced the magnitude and direction of bacterial changes. For example, the same DOM treatment applied at different times during the season resulted in different levels of bacterial production and different bacterial community composition. There was a mid-season shift from Collwelliaceae to Polaribacter having the greatest relative abundance after incubation. This shift corresponded to a modest but significant increase in the initial relative abundance of Polaribacter in the nearshore seawater used to set up experiments. This finding supports a new hypothesis that starting community composition, through priority effects, influenced the trajectory of community succession in response to DOM addition. As strong inter-annual variability and long-term climate change may shift the timing of WAP phytoplankton blooms, and the corresponding production of DOM exudates, this study suggests a mechanism by which different seasonal successional patterns in bacterial communities could occur.

Concurrent jellyfish blooms and tenacibaculosis outbreaks in Northern Norwegian Atlantic salmon (Salmo salar) farms

Tenacibaculosis is an increasing problem in the Norwegian Atlantic salmon aquaculture industry causing significant economic losses. In September 2015, two separate outbreaks of suspected tenacibaculosis occurred at two Atlantic salmon farms in Finnmark County in Northern Norway. The events resulted in major losses of smolts newly transferred into seawater. Prior to, and during the outbreaks, large numbers of small jellyfish, identified as Dipleurosoma typicum (Boeck) were observed in the vicinity of the farms and inside the net-pens. This study investigates the possible link between the jellyfish, Tenacibaculum spp. and the tenacibaculosis outbreaks. Bacteriology, histology, scanning and transmission electron microscopy, and real-time RT-PCR screening were performed on both fish and jellyfish samples. Based on the findings, Tenacibaculum finnmarkense was found to be the dominant bacteria associated with the tenacibaculosis outbreaks at both sites and that D. typicum is unlikely to be a vector for this fish pathogenic bacterium. However, results do show that the jellyfish caused direct damage to the fish's skin and may have exacerbated the bacterial infection by allowing an entry point for bacteria.

The low diverse gastric microbiome of the jellyfish Cotylorhiza tuberculata is dominated by four novel taxa

Cotylorhiza tuberculata is an important scyphozoan jellyfish producing population blooms in the Mediterranean probably due to pelagic ecosystem's decay. Its gastric cavity can serve as a simple model of microbial-animal digestive associations, yet poorly characterized. Using state-of-the-art metagenomic population binning and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH), we show that only four novel clonal phylotypes were consistently associated with multiple jellyfish adults. Two affiliated close to Spiroplasma and Mycoplasma genera, one to chlamydial 'Candidatus Syngnamydia', and one to bacteroidetal Tenacibaculum, and were at least one order of magnitude more abundant than any other bacteria detected. Metabolic modelling predicted an aerobic heterotrophic lifestyle for the chlamydia, which were found intracellularly in Onychodromopsis-like ciliates. The Spiroplasma-like organism was predicted to be an anaerobic fermenter associated to some jellyfish cells, whereas the Tenacibaculum-like as free-living aerobic heterotroph, densely colonizing the mesogleal axis inside the gastric filaments. The association between the jellyfish and its reduced microbiome was close and temporally stable, and possibly related to food digestion and protection from pathogens. Based on the genomic and microscopic data, we propose three candidate taxa: 'Candidatus Syngnamydia medusae', 'Candidatus Medusoplasma mediterranei' and 'Candidatus Tenacibaculum medusae'.

Microbial Surface Colonization and Biofilm Development in Marine Environments

Biotic and abiotic surfaces in marine waters are rapidly colonized by microorganisms. Surface colonization and subsequent biofilm formation and development provide numerous advantages to these organisms and support critical ecological and biogeochemical functions in the changing marine environment. Microbial surface association also contributes to deleterious effects such as biofouling, biocorrosion, and the persistence and transmission of harmful or pathogenic microorganisms and their genetic determinants. The processes and mechanisms of colonization as well as key players among the surface-associated microbiota have been studied for several decades. Accumulating evidence indicates that specific cell-surface, cell-cell, and interpopulation interactions shape the composition, structure, spatiotemporal dynamics, and functions of surface-associated microbial communities. Several key microbial processes and mechanisms, including (i) surface, population, and community sensing and signaling, (ii) intraspecies and interspecies communication and interaction, and (iii) the regulatory balance between cooperation and competition, have been identified as critical for the microbial surface association lifestyle. In this review, recent progress in the study of marine microbial surface colonization and biofilm development is synthesized and discussed. Major gaps in our knowledge remain. We pose questions for targeted investigation of surface-specific community-level microbial features, answers to which would advance our understanding of surface-associated microbial community ecology and the biogeochemical functions of these communities at levels from molecular mechanistic details through systems biological integration.

Discovery, Prevalence, and Persistence of Novel Circular Single-Stranded DNA Viruses in the Ctenophores Mnemiopsis leidyi and Beroe ovata

Gelatinous zooplankton, such as ctenophores and jellyfish, are important components of marine and brackish ecosystems and play critical roles in aquatic biogeochemistry. As voracious predators of plankton, ctenophores have key positions in aquatic food webs and are often successful invaders when introduced to new areas. Gelatinous zooplankton have strong impacts on ecosystem services, particularly in coastal environments. However, little is known about the factors responsible for regulating population dynamics of gelatinous organisms, including biological interactions that may contribute to bloom demise. Ctenophores are known to contain specific bacterial communities and a variety of invertebrate parasites and symbionts; however, no previous studies have examined the presence of viruses in these organisms. Building upon recent studies demonstrating a diversity of single-stranded DNA viruses that encode a replication initiator protein (Rep) in aquatic invertebrates, this study explored the presence of circular, Rep-encoding single-stranded DNA (CRESS-DNA) viruses in the ctenophores Mnemiopsis leidyi and Beroe ovata collected from the Skidaway River Estuary and Savannah River in Georgia, USA. Using rolling circle amplification followed by restriction enzyme digestion, this study provides the first evidence of viruses in ctenophores. Investigation of four CRESS-DNA viruses over an 8-month period using PCR demonstrated temporal trends in viral prevalence and indicated that some of the viruses may persist in ctenophore populations throughout the year. Although future work needs to examine the ecological roles of these ctenophore-associated viruses, this study indicates that viral infection may play a role in population dynamics of gelatinous zooplankton.

Changes in bacterial community metabolism and composition during the degradation of dissolved organic matter from the jellyfish Aurelia aurita in a Mediterranean coastal lagoon

Spatial increases and temporal shifts in outbreaks of gelatinous plankton have been observed over the past several decades in many estuarine and coastal ecosystems. The effects of these blooms on marine ecosystem functioning and particularly on the dynamics of the heterotrophic bacteria are still unclear. The response of the bacterial community from a Mediterranean coastal lagoon to the addition of dissolved organic matter (DOM) from the jellyfish Aurelia aurita, corresponding to an enrichment of dissolved organic carbon (DOC) by 1.4, was assessed for 22 days in microcosms (8 l). The high bioavailability of this material led to (i) a rapid mineralization of the DOC and dissolved organic nitrogen from the jellyfish and (ii) the accumulation of high concentrations of ammonium and orthophosphate in the water column. DOM from jellyfish greatly stimulated heterotrophic prokaryotic production and respiration rates during the first 2 days; then, these activities showed a continuous decay until reaching those measured in the control microcosms (lagoon water only) at the end of the experiment. Bacterial growth efficiency remained below 20%, indicating that most of the DOM was respired and a minor part was channeled to biomass production. Changes in bacterial diversity were assessed by tag pyrosequencing of partial bacterial 16S rRNA genes, DNA fingerprints, and a cultivation approach. While bacterial diversity in control microcosms showed little changes during the experiment, the addition of DOM from the jellyfish induced a rapid growth of Pseudoalteromonas and Vibrio species that were isolated. After 9 days, the bacterial community was dominated by Bacteroidetes, which appeared more adapted to metabolize high-molecular-weight DOM. At the end of the experiment, the bacterial community shifted toward a higher proportion of Alphaproteobacteria. Resilience of the bacterial community after the addition of DOM from the jellyfish was higher for metabolic functions than diversity, suggesting that jellyfish blooms can induce durable changes in the bacterial community structure in coastal lagoons.

Composition of Bacterial Communities Associated with Aurelia aurita Changes with Compartment, Life Stage, and Population

The scyphozoan Aurelia aurita is recognized as a key player in marine ecosystems and a driver of ecosystem change. It is thus intensely studied to address ecological questions, although its associations with microorganisms remain so far undescribed. In the present study, the microbiota associated with A. aurita was visualized with fluorescence in situ hybridization (FISH) analysis, and community structure was analyzed with respect to different life stages, compartments, and populations of A. aurita by 16S rRNA gene amplicon sequencing. We demonstrate that the composition of the A. aurita microbiota is generally highly distinct from the composition of communities present in ambient water. Comparison of microbial communities from different developmental stages reveals evidence for life stage-specific community patterns. Significant restructuring of the microbiota during strobilation from benthic polyp to planktonic life stages is present, arguing for a restructuring during the course of metamorphosis. Furthermore, the microbiota present in different compartments of the adult medusa (exumbrella mucus and gastric cavity) display significant differences, indicating body part-specific colonization. A novel Mycoplasma strain was identified in both compartment-specific microbiota and is most likely present inside the epithelium as indicated by FISH analysis of polyps, indicating potential endosymbiosis. Finally, comparison of polyps of different populations kept under the same controlled laboratory conditions in the same ambient water showed population-specific community patterns, most likely due the genetic background of the host. In conclusion, the presented data indicate that the associated microbiota of A. aurita may play important functional roles, e.g., during the life cycle.